More specifically, the invention proposes a controller for a three-phase brushless motor, comprising: a full bridge circuit, including three circuit branches connected between the two poles of a D.C. voltage supply source, each branch comprising an upper electronic switch and a lower electronic switch, connected with each other and connected to the positive pole and the negative pole, respectively, of said source, each of the windings or phases of the motor being connected to an intermediate point between the two switches of a corresponding branch of the bridge circuit; and an electronic control unit designed to drive, in steady state, the upper switches and the lower switches of the bridge circuit by means of respective sets of three drive signals, said sets of three being offset from each other by about 180 electrical degrees, each set comprising three drive signals offset by about 120 electrical degrees from each other and each comprising an active or conducting portion, alternating with an inactive or cut-off portion; the electronic control unit being designed in such a way that each active portion of each drive signal includes an initial interval of pulsed activation, an intermediate interval of continuous activation, and a final interval of pulsed activation; the intermediate interval of continuous activation having a duration in electrical degrees which is greater than that of each interval of pulsed activation.
A controller of this type is described in EP1845609 A2.
However, controllers of this type tend to produce undesired variations in torque supplied by the motor.